902 THE CEREBELLUM. 



troublesome ; also nystagmus (sometimes lateral, sometimes not). Nystagmus, 

 unsteadiness, and giddiness may be associated, but are often apart, and tliere 

 seems no necessary cerebellar connection between them. 1 Tetanoid rigidity 

 with retraction of the head has been noticed. 2 Illusions of rotatory movement, 

 actual imperative movement of head and eyes to one side, or actual imperative 

 rotation of the body about its own long axis, 3 have been well recorded 

 symptoms, especially where the lesion has been found localised in a middle 

 peduncle. Where the lateral lobe has been the site of lesion, there have been 

 among the symptoms 4 paresis of the homonymous arm and of the legs, and in 

 those limbs instability and tremor in volitional effort ; conjugate deviation of 

 eyes, and of the head away from the side of the lesion ; lateral nystagmus, 

 the jerks being toward the side of the lesion : these signs, co-existing with 

 an intact cutaneous sensibility, and without alteration of psychical condition, 

 compose a series absolutely accordant with Luciani's 5 descriptions of the 

 symptoms in the dog and monkey. Just as, e.g., in Luciani's dogs, the legs are 

 set widely apart, as if to enlarge the basis of support, and the steps taken are 

 abrupt and short. 



Especially valuable from the present standpoint are observations upon cases 

 of atrophy or agenesis of the cerebellum. Occasionally there come to light 

 congenital defects, amounting to absence of one cerebellar hemisphere. 6 In 

 such instances the huge defect has, in more cases than one, occasioned 

 practically no symptoms whatsoever. Movement has been neither uncertain 

 nor tremulous. In one case, the right being the hemisphere lacking, the person 

 had "a habit " of keeping the head turned somewhat to the left ; in childhood, 

 it was stated tliere had been " restlessness " of the head. Of unsteadiness of 

 attitude or of gait, of weakness of the limbs, nystagmus, peculiarity of speech, 

 vertigo, or defective sensation or intelligence, it is certain there was no trace. 

 The knee-jerks were normal and equal right and left. Further, in other 

 instances there has been arrest of growth or atrophy of almost the whole, 

 indeed of the whole, cerebellum. 7 Not a hundredth part of the cerebellum 

 has remained, and yet ability existed to stand, to walk, to handle and lift 

 objects ; in fact, a very fairly normal condition of volitional motility was pre- 

 served. Noteworthy in the records of such cases is absence of detection of 

 any trace of impairment of cutaneous sensibility. The remarkably negative 

 character of even extreme cases of atrophy or agenesis is paralleled by the 

 frequency with which cerebellar lesions of even large size but non-irritative 

 type await unsuspected a post-mortem revelation. 



Inferences regarding function of the cerebellum drawn from 

 comparative anatomy.— Unlike that of the cerebral hemispheres, the 

 development of the cerebellum does not consistently and directly increase 

 with progress upward in the grades of animal hierarchy. The cerebellum is 

 found developed in extremely various degree in closely allied forms. Many 

 forms higher, on general grounds, have simpler cerebella than some which 

 are much lower. The crawling reptiles possess less cerebellum than the 

 great swimmers, the Teleosteans and Selachians. In birds the cerebellum 

 is relatively enormous, but even in them it consists entirely of the median 

 vermis. In mammals the lateral lobes appear, small in the Marsupials, 

 larger in the Carnivora, largest in the apes and man. The lateral lobes have 



1 Gowers, "Diseases of the Nervous System," London, 1886, vol. ii. 



2 Hughlings Jackson, Medical Mirror, London, 1869. 3 Magendie, loc. cit. 



4 Acland and Ballance, St. Thomas's Hosp. Rep., London, 1S96, vol. xxiii. 



5 Loc. cit. 



6 Lallement's ease, Bull. Soc. anat. de Paris, 1862 ; Hitzig's case, Arch, de neurol., Paris, 

 1884 ; Neubiirger and Edinger's ease, Berl. klin. Wchnschr., 1898, S. 69. 



7 Combettes, Bull. Soc. anat. de Paris, 18-31 ; Shuttleworth, Brit. Med. Journ , London, 

 1885, etc. 



